1. Field
The present invention relates generally to processing of seismic data to remove artifacts and particularly to artifacts resulting from near surface filtering effects and ghost reflections.
2. Background
During the last 25 years, the oil and gas industry has sought to gain more subsurface property information from seismic data. In particular, it is desirable to obtain detailed information about subsurface pore fluids, porosity, lithology, pressure and geometry. In order to glean this information from seismic data, it is necessary to compensate for a variety of effects that tend to obscure the nature of the subsurface properties under investigation.
Among the effects of interest are those that are due to near surface conditions including, for example, ghosts or layering contrasts. For near offset measurements, the reflected signal should undergo near surface filtering in conformance with a convolutional model of seismic data (i.e., it should be possible to model the received signal as a time invariant wavelet convolved with the earth reflectivity). Where larger offsets are involved, each arriving reflection undergoes a different near surface filtering effect that is determined by local near surface geology and the initial and arrival angles of wavefronts at the source and receiver locations.
Existing models generally make use of an assumption that near surface filters have effects that are independent of wavefront takeoff/arrival angles. Other methods may be limited by spatial aliasing and truncation effects of the 2D or 3D common source and receiver gather transforms (tau-p or slant stack, for example) that directly estimate emergence angle responses for all angle event.
Accordingly, the inventors have determined that the present invention may allow for an improved compensation for near surface effects when analyzing seismic data representative of subsurface geological structures and properties.